In recent years, due to improvement in performance of high performance electronic equipment, a heat generated by circuit components (for example, circuit component such as an MPU) installed in the electronic equipment is on a steady increase. Therefore, due to the increased heat of the circuit components, a temperature within a housing of the electronic component increases greatly. Thus, a cooling fan is used for cooling the inside of the housing of the electronic component and the circuit components.
A conventional cooling fan includes a rotor portion, an armature and a base portion. The rotor portion includes an annular rotor magnet, and an impeller arranged in a circumferential direction centering a central axis of the rotor portion. The armature is affixed to the base portion so as to radially oppose the rotor magnet. The armature includes a plurality of teeth each extending in a radial direction. A magnet wire is wound around each tooth via an insulator in order to form a coil around each tooth. When the magnet wire is wound around the teeth, a predetermined amount of tension is imparted on the magnet wire. In general, the coil has the magnet wire which is wound around the teeth wherein the magnet wire has a predetermined tension so as not to slack. The tension provided to the magnet wire becomes greater when a diameter of the magnet wire is greater. The magnet wire which forms the coil is electrically connected via a conductive pin to a circuit on which the circuit components are mounted in order to control a rotation of the rotor portion. The conductive pin is affixed to the insulator. The magnet wire which forms the coil is wound around the teeth, wound around the conductive pin without slack, and then is soldered to a circuit board. Since the conductive pin is soldered to the circuit board, the magnet wire and the circuit board are electrically connected to one another. A drive current is supplied from an external source to a control circuit, an electric current is conducted through the magnet wire wound around the teeth, and then, a magnetic field is generated at a radial gap between the teeth and the rotor magnet. As the magnetic field is generated, the teeth and the rotor magnet attract one another, and repel one another. Due to such interaction between the teeth and the rotor magnet as described above, a rotary torque centering about the central axis is generated in the rotor portion.
Due to the great deal of increase in the temperature within the electric component, there is a further demand for cooling within the electric component. Therefore, there is an increased demand for a cooling fan having a cooling characteristic superior to that of the conventional cooling fan. In general, in order to improve the cooling characteristic of the cooling fan, a flow quantity of the cooling fan needs to be improved so as to increase a volume of heated air exhausted from the housing of the electric component. In order to improve the flow quantity, an air flow which is generated when the impeller rotates needs to be increased, which consequently increases a work load of the impeller and therefore a current value of the electricity supplied to the cooling fan becomes high. When an electric current is conducted to the magnet wire wound around a stator core, an electric resistance of the magnet wire causes the increase in the temperature of the magnet wire. When the electric current conducted to the magnet wire is high, the increase in the temperature of the magnet wire is further increased.
Conventionally, when designing a motor of a high speed rotation, a magnet wire having a low electric resistance is used. That is, when designing a motor whose impeller, when being rotated, is expected to perform a great deal of work load (i.e., flow quantity of air flow generated in accordance with the rotation of the impeller), a magnet wire having a diameter greater than the conventional diameter is used. However, when the magnet wire having the greater diameter is wound around the teeth, tension imparted on magnet wire is conducted to the conductive pin, stressing the conductive pin excessively and increasing the possibility of slackening the conductive pin. When the conductive pin is not used (e.g., a land formed at the circuit wiring configuring the control circuit is used), the magnet wire forming the coil is directly soldered to the land. When the magnet wire is soldered to the land, it is preferable that the neither the magnet wire nor the coil is soldered without being slackened. In order to solder the magnet wire or the coil without having them slackened, the magnet wire and the coil need to be soldered while tension is applied thereto. However, the tension applied to the magnetic wire and the coil may be eased however slightly, and therefore, the magnetic wire and the coil are slackened. Therefore, it is a difficult task to solder the magnetic wire forming the coil without allowing the magnetic wire to be slackened. The slack formed on the magnetic wire is conducted, due to vibration of the motor, to the coil, and thereby forming a slack on the coil. Once a slack is formed on the coil, there is a possibility that the magnetic wire comes off the coil, comes into contact with a rotor arranged axially above the coil, and then is damaged.
In view of the above problem, a following configuration is disclosed according to a cooling fan shown in FIG. 1 of a Patent Document 1. An annular wire holder includes a hook portion which protrudes toward a central axis from a radially inner edge portion. A magnet wire is hooked on the hook portion of the wire holder. By virtue of such configuration, a coil wire will be handled with facility.
[Patent Document 1] Japanese Patent Publication No. 3127916 (FIG. 1)